Actuators are used to control the operation of many valves and other fluid components, whether liquid, gas or a combination thereof. The actuator may be of any number of different designs including pneumatic, hydraulic, electric and so on. Piston type actuators use pressurized fluid, such as air, to move pistons in order to open and/or close the fluid component. Actuators may use multiple pistons to allow for additional surface area for the pressurized fluid to act upon, thereby increasing the force output of the actuator. Using multiple pistons, however, typically increases the overall height of the actuator, which may preclude use of the actuator in certain applications.
Known actuator designs are acceptable for many applications, though they tend to have a relatively limited cycle life. With faster cycling valves, such as an ALD (Atomic Layer Deposition) valve, the standard valve life may be reduced to only weeks. Recent efforts to increase the diaphragm cycle life on these type of valves have resulted in the actuator being the limiting factor for cycle life of the actuator/valve assembly. This is particularly pronounced when the actuator is subjected to very high cycles such as in the tens of millions. Such high cycle specifications are becoming more common in industries such as semiconductor processing, for example. The intricate processes for making semiconductor devices necessitates very high cycle lives.
Actuators that utilize multiple pistons are also susceptible to limited cycle life. For known multi-piston actuator designs, a common end of cycle life limitation results from the top piston cocking (or tilting) due to uneven spring force. The piston cocking results in metal-to-metal contact where the top piston engages a cap or a housing and forms a sliding seal. The galling action resulting from the metal-to-metal contact may produce metal chips and rough surfaces, which wear the seal causing leakage or stalling of the actuator.